cos^2(x)

#include <stdio.h>
#include <math.h>

int main()
{
    int k = 0;
    double x, e, d, s;

    printf("x = ");
    scanf("%lf", &x);
    printf("e = ");
    scanf("%lf", &e);
    printf("cos^2(%e) = ", x);

    while (31.416 < x) {
        x = x - 31.416;
    }
    while (x < -31.416) {
        x = x + 31.416;
    }

    s = 1;
    d = 1;
    while (e < fabs(d)) {
        k = k + 1;
        d = (-d) * x * x / ((2 * k - 1) * (2 * k));
        s = s + d;
    }

    printf("%e\n", s*s);
    printf("%3.3e",(pow(cos(x), 2)));

    return 0;
}